The present invention is related to an ion beam processing apparatus, and in particular, to an ion beam processing apparatus which is suitable for processing a work piece by etching with a large current and a large diameter ion beam.
As a prior art ion beam processing apparatus, there is known, for example, an etching apparatus for etching a work piece using an ion beam as disclosed in JPA Laid-Open No. 63-157887. In this apparatus, in order to prevent for the work piece charged by the ion beam irradiated thereon from being damaged due to its charging, an ion beam neutralizing method is employed, wherein a plasma is generated by a microwave discharge in a neutralizing unit disposed near to the ion beam, and electrons are supplied from the plasma through a small opening to the ion beam so as to neutralize the ion beam. This method assures a longer time of operation compared to an ion beam neutralizing method which uses a hollow cathode containing a filament for emitting thermoelectrons, and thus is suitable for neutralizing a reactive ion beam. Further, because no filament such as tungsten is used, contamination of the work piece by heavy metals constituting the filament can be prevented, thereby providing for a clean ion beam processing.
However, the conventional neutralizing method has a limitation in providing for a large current and large diameter ion beam because of the following reasons to be described below.
When providing for a large current ion beam, it becomes necessary also to increase a flow of electrons to be supplied from the neutralizing unit in order to effectively neutralize the large current ion beam thus increased. However, according to the conventional method whereby electrons are supplied from the plasma produced within the neutralizing unit, a same quantity of ion current as an increase in the large current ion beam must be collected within the neutralizing unit. That is, an increase in the flow of electrons to be supplied means that the ion current to be collected also increases. In addition, in order for a higher density plasma to be generated within the neutralizing unit, it becomes necessary to increase the power of a microwave to be input into the neutralizing unit, consequently increasing a plasma potential in the neutralizing unit. This means an increase in collision energy of ions to be collected in the neutralizing unit. According to the conventional method as described above, with increases in the ion current colliding on the internal wall of the neutralizing unit and in the ion energy, conducting particles sputtered from the internal wall of the neutralizing unit by ion bombardment are caused easily to deposit on a microwave inlet window of the neutralizing unit, thereby substantially limiting a service life of the neutralizing unit.
Further, in order to extract a large quantity of electrons into the processing chamber, it becomes necessary to decrease a potential of the neutralizing device itself to a negative potential which is far below compared to that of the processing chamber. Consequently, the energy of electrons having been extracted from the neutralizing device becomes greater, thereby distorting a distribution of potentials in the ion beam, and thereby causing to diverge the ion beam which inherently must be parallel. Still further, because the site of supply of electrons to the ion beam is localized according to the conventional method, its spatial uniformity effect of neutralization is deteriorated with an increasing diameter of the ion beam.
From the reasons described above, it has been difficult according to the conventional methods to obtain a large current, large diameter ion beam with a minimized divergence, which is in excess of 300 mA and 200 mm in diameter, and which is uniformly neutralized.
Hence, in order to solve these problems, there has been proposed a microwave neutralizing device for use in an ion beam processing apparatus as disclosed in JPA No. 8-296069, which utilizes a multi-cusp magnetic field formed between electron cyclotron resonance magnetic fields, and into which a microwave is introduced through a wave guide to form a plasma therein. This plasma is used as a source of low energy electrons.